So what accounts for the disparity between this poll and the earlier Zogby? Methodology, MOE, and question phrasing. For example, this poll obviously pushed people to make some sort of decision (thus including "leaners"), as evidenced by the low 12 percent undecided result. That earlier Zogby poll allowed more respondents to remain uncommitted, eliminating leaners and resulting in a much larger 39 percent undecided result.

Ulimately, it's impossible to compare polls against each other. Remember, it's the trends across the same polls that are important.